In general, a cellular radio communication system covers a wide service area by dividing the wide service area into units of communication areas called cells and equipping each of the communication areas with a radio base station in charge of radio communications with a radio terminal in the communication area.
Meanwhile, in radio communication systems based on one-cell frequency reuse, i.e., in radio communication systems in which adjacent radio base stations use the same frequency, a radio terminal located in an edge of the communication area (cell edge) is mainly affected by interference from a radio base station in an adjacent communication area (hereinafter, an adjacent base station), and therefore has the throughput of in the downlink communications reduced.
For the radio communication systems of the aforementioned kind, there are known a method to avoid the interference by designing the communication areas strictly, a method to avoid the interference by adjusting antenna tilt angles and the like at the time of installing the radio base stations (hereinafter, a first background art).
Furthermore, a method called frequency scheduling is known (hereinafter, a second background art). In the frequency scheduling, a frequency with which a radio terminal is less affected by the interference from an adjacent radio base station is allocated to the radio terminal. To put it more specifically, the radio terminal measures a reception quality (received SINR, for example) for each frequency and then reports a CQI (Channel Quality Indicator) indicating the measurement result to the radio base station. The radio base station allocates a frequency less affected by the interference from an adjacent radio base station to the radio terminal in accordance with the reported CQI (refer to Non-PATENT DOCUMENT 1).